The K562 human leukemia cell line has been used in our laboratory as a model system for the study of human erythroid differentiation and globin gene expression. We have shown that hemin causes induction of hemoglobin synthesis by increasing mRNA levels and that this process is fully reversible, without evidence of terminal differentiation. We have studied the physiological properties of the embryonic and fetal hemoglobins synthesized in these cells as a response to hemin. We find that following induction of hemoglobin synthesis K562 cells demonstrate oxygen dissociation properties similar to human embryonic red cells. The P50 value of the hemoglobin is 20 (plus/minus) 0.9 mmHg. The Hill coefficient is 2.5. Intracellular pH of K562 cells, measured by 31-P NMR, is 7.3. The influence of temperature on P50 value of the hemoglobin is similar to that of normal red cells. We also find that the levels of 2,3-diphosphoglycerate (DPG), a potent modifier of hemoglobin function, increase dramatically upon the induction of hemoglobin synthesis in K562 cells. In a typical experiment, DPG levels went from 8 nmoles/108 cells to 64 nmoles/108 cells upon induction of hemoglobin. For several experiments there was an approximately linear relationship between DPG and hemoglobin levels. The coordinate increase in DPG and hemoglobin levels has been demonstrated not only by an enzymatic method but also by 31-P NMR spectroscopy. These data suggest that DPG and hemoglobin levels are coordinately controlled in these cells. We are now investigating the molecular mechanism of the coordinate increase in DPG and hemoglobin levels in response to hemin induction.